To meet the demand for higher integration density and operating speed of LSIs, the effort to reduce the pattern rule is in rapid progress. As the advanced miniaturization technology, manufacturing of microelectronic devices at the 45 to 32 nm node by the ArF immersion lithography has been implemented in a mass scale. The candidates for the next generation 32 nm or finer node include ultra-high NA lens immersion lithography using a liquid having a higher refractive index than water in combination with a high refractive index lens and a high refractive index resist film, extreme ultraviolet (EUV) lithography of 13.5 nm wavelength, and double patterning version of the ArF lithography, on which active research efforts have been made.
Besides the positive tone resist by alkaline development, a highlight is recently put on the negative tone resist by organic solvent development. It would be desirable if a very fine hole pattern, which is not achievable with the positive tone, is resolvable through negative tone exposure. To this end, a positive resist composition featuring a high resolution is subjected to organic solvent development to form a negative pattern.
As the ArF resist composition for negative tone development with organic solvent, positive ArF resist compositions of the prior art design may be used. Such a pattern forming process is described in Patent Document 1.
Independent of whether the resist material is subject to positive or negative tone development, the resist material must have a high sensitivity and resolution and form a resist pattern tenaciously adhered to the substrate, referred to as substrate adhesion, hereinafter. As the unit capable of providing substrate adhesion, heretofore, methacrylate units of monocyclic lactone type such as butyrolactone or valerolactone ring and methacrylate units of fused ring lactone as typified by norbornane lactone have been proposed (see Patent Documents 2 to 4). Sultone units having a cyclic sulfonic acid ester structure are also used for the same purpose as the lactone units (see Patent Document 5).
To meet the further miniaturization requirement, there is a desire to have a base resin unit capable of displaying improved properties including sensitivity, resolution, control of acid diffusion length, and substrate adhesion.